This invention relates to data storage devices, and particularly to data storage devices employing rotating storage discs, such as magnetic, magneto-optical and optical disc drives.
Most disc drives employ recording techniques known as zone bit recording by which the data recorded in different radial zones are recorded at different data frequencies so that the data density along the concentric tracks is substantially the same in all zones on the disc. More particularly, data are recorded at higher frequencies in outer zones, where the tracks are longer and the lineal velocities are greater, so that the data density is substantially the same in the outer zones as in the inner zones. All tracks in a given zone are recorded at the same frequency, with different recording frequencies assigned to each zone. For example, if a disc contains ten radial zones, there are ten distinct recording patterns, one for each zone, each having a distinct data frequency. Data density is usually expressed in numbers of bits of data per inch (BPI) along the track. Because all tracks within a given zone have the same data frequency, there is a slight variation of the data density between the inner track of a given zone and the outer track of that zone. Notwithstanding the slight variances of data density within a zone, the data density is substantially the same in all zones. Usually the data density for a zone is established by that of the inner-most track of the zone, which has the highest density for the zone. Consequently, the data densities on the inner-most tracks of each zone is usually the same for all of the zones on the disc surface.
Each track includes a plurality of data sectors. Usually all of the data sectors contain the same number of bits, regardless of the track or zone. Hence, the sectors are of equal length, in terms of numbers of bits, and are substantially equal in physical length due to the substantially equal data density. Consequently, the tracks in outer zones contain a greater number of sectors than tracks in inner zones.
Currently, disc drives include a zone table for each recording surface that defines the zones and specifies a BPI setting for the surface. The BPI setting is an expression of the data density, establishes the data frequency for each zone on the surface and the number of sectors per track for each zone. The BPI setting is a standardized setting that establishes the data density, in terms of bits per inch (BPI), for all the entire disc surface. Each BPI setting references a table of data frequencies and numbers of data sectors, for the tracks of each zone. Currently, a single BPI setting is employed for a recording surface, although a given disc drive may include a combination of BPI settings, one for each head/surface combination in the drive.
During qualification of a disc drive, tests are conducted to ascertain that the drive meets required specifications. When a drive fails the qualification test due to poor error rates of recovering data from the recording surface, the drive must be re-worked. In some cases, these poor error rates may appear only from certain zones on the recording surface, and may be due to weak head/surface combinations in those zones. There exists a need to relax the data densities and frequencies in these zones, thereby reducing stress on the heads and improving error rates, and maximizing production yields. Other features and benefits that characterize the present invention will be apparent upon reading the following detailed description and review of the associated drawings.
In one embodiment, a recording surface of a disc drive that failed to meet a predetermined error rate is re-formatted. The recording surface is segmented into a plurality of radial zones each containing a plurality of concentric tracks on which data may be recorded. The recording surface is originally formatted with a data frequency for each zone such that all of the zones have substantially the same data density. The data frequency is reduced for a first zone whose error rate is greater than the predetermined error rate, and is increased for a second zone whose error rate is less than the predetermined error rate.
In preferred embodiments, the second zone is the zone having the best error rate. The data storage capacity of the recording surface having zones of increased and decreased data density is identified and compared to a required data storage capacity. The second zone data density is increased to increase the data storage capacity of the recording surface to meet the required data storage capacity. Hence, the increased data density of the second zone provides increased data storage capacity to compensate for loss of data storage capacity due to reduction of the data density in the first zone.
In another embodiment, a disc drive has at least one disc having a recording surface segmented into a plurality of radial zones containing pluralities of concentric tracks on which data may be recorded at a data frequency. The data density of tracks in at least one zone is substantially different from the data density of tracks in at least one other zone. More particularly, the recording surface has a nominal data density for all zones that defines a minimum data storage capacity for the recording surface. The data density in a first zone is substantially less than the nominal data density, and the data density in a second zone is substantially greater than the nominal data density. The data storage capacity of the recording surface is at least as great as the minimum data storage capacity.
Other features and benefits that characterize the present invention will be apparent upon reading the following detailed description and review of the associated drawings.